There have been many attempts in the past to maintain liquids and solids within certain temperature ranges. Hot beverages are usually prepared and served at temperatures well above the temperature at which consumers prefer to drink them. Typically, the consumer must wait an extended period for the beverage to sufficiently cool before drinking it. Some impatient consumers will attempt to drink the beverage too soon resulting in burns to the mouth. Similarly, if the drink is spilled before it has had sufficient time to cool, burns to the skin may result. Therefore, it is desirable to rapidly cool the beverage from the temperature at which it is served to an acceptable drinking range. Once the beverage is within the acceptable drinking temperature range, it is desirable to maintain the temperature of the beverage within this range for an extended period of time.
Many approaches have been tried for both rapidly cooling a hot beverage and for maintaining the temperature of the beverage within an acceptable drinking temperature range. To rapidly cool a hot beverage, ice or a cool liquid (e.g., water or milk) can be added to the hot beverage. This approach rapidly cools the beverage but dilutes the hot beverage. This is frequently undesirable. This approach is often inconvenient and imprecise; if the person adds too little or too much, the temperature of the hot beverage will be higher or lower than desired and may require further attention. Finally, this approach does not provide any assistance in maintaining the temperature of the hot beverage in the acceptable drinking temperature range. Once the beverage reaches an acceptable temperature, it will continue to lose thermal energy to its surroundings. This results in the beverage becoming cool too quickly. Therefore, the beverage remains within an acceptable drinking temperature range for only a short period.
A hot beverage can also be cooled by pouring it into a cool container. Thermal energy is transferred from the hot beverage to the cool container thereby warming the container and cooling the beverage. This approach suffers from some of the same limitations as adding cool liquid or ice. If the cup is too cool or too warm or has too much or too little thermal mass, the beverage will stabilize at the wrong temperature. Also, while a heavy container will slow the rate of cooling somewhat due to the increase in the total thermal mass of the system, the effect will be small and the beverage will only remain in the ideal drinking range for a short period.
Up to this time, the primary method employed for slowing the cooling rate of a beverage was to insulate the container. Everything from simple foam cups to expensive and sophisticated vacuum mugs is used. These approaches slow the cooling rate of the beverage. However, the ability of the insulated mugs currently on the market to maintain beverage temperatures is relatively limited. Even the best mugs usually keep liquids warm for less than 45 minutes. Stainless, vacuum insulated mugs are best at maintaining temperature, but no product currently exists which can passively cool a hot beverage quickly. Also, the beverage in an insulated container will continue to cool despite the insulation. The cooling rate will only be slowed. Insulation does not provide a way to add thermal energy back to the beverage.
To maintain the temperature of a beverage as it cools, the prior art has taught the use of an electric heater. At least one manufacturer produces a portable refrigerator/heater which plugs into a car's cigarette lighter and may be used to cool or warm beverages. Likewise, plug-in mugs, hot plates and immersion devices may be used to keep beverages warm. Some beverage containers are available that plug into accessory plugs in automobiles. A container may also be periodically microwaved to reheat the contents. All of theses approaches suffer from lack of portability and dependence on outside energy sources. They also fail to address the need to rapidly cool a beverage to an acceptable drinking temperature range.
The demand for hot beverages is very high, especially for coffee and tea, the most popular adult hot beverages. In 1990, approximately 42% of the US population consumed coffee and 30% consumed tea. The number of occasions that hot beverages are consumed away from home has increased significantly in recent years. By 1999, the Specialty Coffee Association of America predicts that there will be approximately 10,000 coffee cafes in comparison to the approximately 3,000 in 1996. The Association forecasts that of the $1.5 billion in sales coffee cafes will ring up in 1999, 20% will be from hot beverage take out.
Therefore, it is desirable to develop a reusable beverage container that will rapidly cool a beverage to an acceptable drinking temperature, will maintain the temperature within an acceptable temperature range for an extended period, requires neither manipulation by the consumer or the input of external energy, and is portable.
Another related application requiring temperature regulation is baby bottles. Beverages given to infants usually must be warmed but it is important to not give an infant a beverage that is too hot. Infants cannot tolerate temperatures as high as adults and parents must learn to determine the maximum acceptable temperature for their child. Therefore, when a beverage is warmed for an infant, it may be necessary to cool it rapidly back to an acceptable temperature. If the beverage is too warm, a parent typically must add cool liquid or allow time to pass. Also, if the infant is fussy and does not drink the entire contents of the bottle immediately, the contents may cool to the point that the infant will not drink it. Then the parent must reheat the bottle being careful to not overheat it. Insulated baby bottles are available which extend the time the contents are acceptably warm but they fail to add thermal energy back to the bottle contents. Therefore, it is desirable to develop a baby bottle that will rapidly reduce the temperature of a beverage to a safe drinking temperature for an infant and then will maintain that temperature for an extended period.
Another application where it is desirable to regulate the temperature of a liquid is in bathing tubs. When a person takes a bath or soaks in a tub, the water must be within a certain range to be comfortable. If the water is too hot, the person may be unable to enter the water or may be injured by it. This is especially important with infants and small children. If the water is too hot, cold water must be added until the temperature falls in an acceptable range. Once the water is at an acceptable temperature, it is desirable to maintain its temperature for the period of the bath. If a person wishes to soak or a child wishes to play in the tub for a period of time, the water may become uncomfortable due to its falling temperature. Then, additional hot water must be added to raise the temperature back into the acceptable range. Insulated bathing tubs are available which help reduce the rate of temperature loss but do not address the issue of water that is too hot. They also fail to add thermal energy back into the tub. Some whirlpool tubs include heaters for maintaining the temperature of the water but these devices are expensive to purchase and operate, require a complex system of pumps, valves and switches, and are noisy in operation. They also fail to address the issue of water that is too hot. Therefore, it is desirable to develop a bathing tub that would rapidly reduce the temperature of water to an acceptable bathing range and then to maintain the temperature of the water within the acceptable range for an extended period.